2 The coefficient of \(x ^ { 4 }\) in the expansion of \(( x + a ) ^ { 6 }\) is \(p\) and the coefficient of \(x ^ { 2 }\) in the expansion of \(( a x + 3 ) ^ { 4 }\) is \(q\). It is given that \(p + q = 276\).
Find the possible values of the constant \(a\).